Selective reception of telegraphic signals



' H. J. J. M. DE REGNAULD DE BELLESCIZE SELECTIVE RECEPTION OF TELEGRAPHIC SIGNALS Filed May 27, 1932 2 Sheets-Sheet 1 Fig 1 11 11 f 1- "21 22" we 2?:- E5 237 22 2a If? as 22,692

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H. J J. M. DE REGNAULD DE BELLE SCIZE SELECTIVE RECEPTION OF TELEGRAPHIC SIGNALS Filed May 27, 1932 2 Sheets-Sheet 2 icxs l l- -=l l l-l'l l l l lgl l l l-l+l- 4 Lu-NJ v Y Z22 bezel??? 6Z9 Fey 22206 27? ZQ fieZieacize Patented Jan. 15, 1935 UNITE -STA ES PATENT OFFICE ssmcrrva nucngitgg gr mmcaarmc Henri Jean Joseph Marie -de Regnanld dc Bellcsciae, Neuilly-sur-Seine, France Application May 27, 1932, Serial No. 013.940

In France May 29, 1931 '4 Claims. (01. ii-as) My invention relates broadly to printing teletransmitted signals the proper signal wave of graph systems and more particularly to amethod frequency I which is intended for a given reof selectively receiving printing telegraph sigceiving apparatus. nals and an improved circuit arrangement for with regard to the statics, the rules of accumuoperation by the received printer signals. lation by'resonance, the use of which will be 5 The method according to the invention has ameliorated by the present invention, are defor its object to improve the utilization of sigfined as follows by Ernst F. W. Alexander-son in nals consisting of unit signs or elements such as the United States Patent No. 1,465,961, (page 1, dots and spaces, all of which have an equal lines 29-44):

l0 duration. The Baudot telegraph system, for in- According to the law of probability, the acl0 stance, corresponds to this condition, since its cumulative effect of successive static shocks in alphabet in order to represent the different letany oscillating circuit increases by the square ters and figures, employs combinations of five root of the time in which theirregular shocks dots or spaces of equal duration. As a series of are taking place, whereas the oscillations due to several dots in succession and without interrupthe signal, if this is a continuous wave increase 15 tion is equivalent to a dash, it may be further arithmetically until the circuit has approached stated that the present invention applies to all its maximum amplitude; thus the relative in signals consisting of unit signs or elements whose tensity of the signal and the static is greater the duration is an integral multiple of a given interlonger the time during which the energy of the '20 val of time. Itis a known fact that such a sigsignal can accumulate."

nal may be transmitted by employing in the From the point of view of the utilization of transmitting station a rotary distributor operatthis rule, ordinary receivers contain three im- 1 ing at constant speed, and it may be received perfections which are entirely remedied by the by employing in the receiving station a second present invention. The first of these imperfecrotary distributor which is maintained at the tions is as follows": In prior forms of receiving as proper angular setting withreference to the circuits the resonance, which is the means emtransmitting distributor by suitable correcting ployed to accumulate the successive impulses means. It is also a known fact that each dot, produced bythe consecutive cycles of the oscilwhose duration is constant, may consist of a lation to be received, effects this accumulation :zo wave or a sinusoidal oscillation having a certain in a very imperfect manner. In fact, various so frequency f. It will, therefore, be unnecessary factors make it necessary to give to the resonato describe these various details, as they are tors time-constants which are much smallerthan matters of common practice, and are chiefly the duration of the oscillation, but by the methused in wire or radio telegraph systems by the ad of my invention, the accumulation is effected use of the Baudot or derived systems. to the total amount, as it takes place in a circuit 36 The present invention relates to a method for whose time-constant much exceeds the duration the reception of such signals, each dot of which, of the oscillation. i having a constant duration, is transmitted by The second imperfection is as follows: In the means of a m k Wave, whose requency I is prior forms of receiving circuits, the current due 40 s p o t h frequency of the unit signs, i. e. to the accumulation by resonance is utilized in 40 to the number of these unit signs per second. proportion as ltis established in the resonator, This method essentially consists in placing in the and thus the effectiveness of this current depends receiving apparatus a device selecting thisfreupon its mean amplitude, which is much less quency f, and constituted so as to insure to the than its maximum amplitude. In the method signal. wave the best protection which can be of my invention, on the contrary, the accumula- 5.

obtained against interfering waves and statics, tion is utilized only at the exact moment when according to the rules of accumulation by it reaches its maximum amplitude. resonance. The third imperfection is as follows: In the With regard to interfering waves, this feature prior forms of receiving circuits the accumuof the present invention will co ist in the selative effects respectively produced in the select- 50 lecticn of the wave frequency f in a device, for ing device by the static and signal wave do not instance a resonator, whose time constant vexact in thesame way on the recording relay; the ceeds considerably the duration'T of each markaction of the static isrendered unnecessarily ing wave. This method leads us to a new means dangerous. In fact when the disturbances are for selecting from a number of simultaneously practically continuous, which is often the case for atmospheric disturbances, they will produce a forced current in the receiving resonators, and it is the mean value of this current that actuates the recording relay. On the other hand, each dot of the signal energy acts upon the relay in the manner of an impulse, and especially when a the keying is very rapid. The effectiveness of of the recording are the same for the signal said sign. This is the best result which it ispossible to obtain theoretically by making use of the mechanism of accumulation by resonance. The said result could be obtained by making use of a resonator tuned on the frequency 1 of the signal "wave, and having a time constant superior to the duration of each -unit sign. Butfor practical reasons, I prefer using homodyne reception which consists in combining the receivedwaves with an auxiliary oscillation whose phase diflerence with the signal wave which is to be received,

is approximately constant. It is known that this combination transforms each marking wave of the signal into a direct current and each interfering marking wave into an undesired current which is sinusoidal, and thestatics into anundesired current varying at random, the intensity of the same current having the same chance of g being positive or negative. If these currents are afterwards passed through an aperiodic circuit having a sufficiently great time constant, nearly the whole quantity of electricity produced by the said directcurrent is accumulated in the condenser ofthe aperiodic circuit, and the ratio existing between this accumulative effect and the accumulative eflects of the said undesired currents is exactly the same as if the said received oscillation had been passed through a resonator 'tuned onthe frequency f and-having the same time constant as the aperiodic circuit, but in addition to the fact that a large time-constant can be more readily obtained by the use of an aperiodic circuit, the reception of the signal by means of a local synchronous oscillation has in itself numerous advantages; for instance, the density of the aperiodic disturbances is reduced" by, one-half by their combination with the auxilia'ry oscillation, and again, the transmitting station can be better utilized, by employing, for the dots. and spaces of the alphabet, marking and,

spacing wave of the same frequency but opposite in phase. By combiningthus the advantages belongingin particular to homodyne reception with thosedue particularly to the present method ofmaking use of resonance, the gain in the signal noise ratio exceeds 15 decibels at low "speeds of keying and increases rapidly at hi speeds.

In the method of my invention, a higher degree of selectivity is also obtained with regard to the elimination of interfering signals. When a certain number of signals are simultaneously transmitted on different carrier frequencies each of which is intendedfor a given receiver, it is a known fact that a certain diflerence must be allowed between the respective frequencies given to these signals, in order that each receiver may distinguish the signal intended for the individual receiver. As an example, if the dots and spaces whose combination forms the alphabet each have a duration of 1/50 second, that is, if eachsignal has 50 such unit signs per second, in prior forms of receiving methods it is necessary to allow a difference of at least 250 periods between the frequencies respectively given to the signals. The method of my invention permits a reduction of this difference to about 50. periods, and hence provides a system which allows the simultaneous transmission of 11% times the usual number of messages between two limiting frequencies. This result is obtained by establishing, between the duration of the unit signs depending upon the rate of rotation of the distributors, and the difference allowed between the frequencies, a certain relation such that this difference will be practically an integral multiple of the frequency of the unit signs of each signal. In the preceding example, the frequencies allotted to the respective signals will thus be practically equal to f, f+50. f+100, f+150, periods. This feature will be further brought out in the description of the apparatus as the specification continues.

The method and circuit arrangement of my invention will be more fully understood from the specification hereinafter following by reference to the accompanying drawings, in which:

Figure 1 shows the division of the time into equal intervals as effected by the rotary distributors in the transmitting and the receiving stations of a line wire or wireless communication system; Fig. 2 represents the oscillation whose frequency is ,f and which constitutes any one of the dots of the signal to be received; Fig. 3 is a circuit arrangement of the'apparatus by which the signal is received and recorded and distinguished from undesired disturbances; Fig. 4 represents the direct current produced in the said receiving apparatus by the homodyne reception of the signal wave shown in Fig. 2, this homodyne reception being obtained by combining the said wave with an auxiliary oscillation having the same frequency and phase characteristics; Fig. 5 represents the electrostatic charge which this current accumulates in the condenser of the receiving apparatus'and the curve of discharge of .the said condenser in a recording relay; Fig. 6 shows the sinusoidal current produced in the receiver of Fig. 3 when the local oscillation, having the same frequency as the signal to be received, is combined with the oscillation produced by an interfering signal which is not intended for the same receiver; and Fig. 7 represents the electrostatic potential which the said sinusoidal current accumulates in the condenser of the receiving apparatus, this'potentia'l being null at the final instant,-the interfering wave being eliminated when -into equal intervals, wherein the units (dots or spaces) are distributed according to the characters in the text of the telegram to be transmitted. The time interval 1-2 may for instance contain a dot, which consists of the oscillation 5 (Fig. 2) this oscillation whose frequency is f, commences at the instant 1 and ceases at the instant 2. The next interval 2-3 may contain a like oscillation, if a dot is to be transmitted, or it may be occupied by a space, and soon for the rest of the time intervals. Fig. 3 shows a, preferred circuit arrangement embodying my invention and wherein the signal oscillation 5 is utilized to actuate the recording relay. The electron tube detector '7 has an input circuit 44 including the secondary windings of transformers '45 and 46. The input to these transformers receive at the same time at 6 and 8 two oscillations of the same frequency and phase characteristic. The oscillation entering at 6 is the one shown in Fig. 2 which constitutes the dot of the signal energy to be recorded. This oscillation, which is received by wire or through the ether has in the first place traversed the devices (not shown) constituting an ordinary receiver, such as an amplifier, a band-pass filter, etc., and its frequency may have been changed by one or more heterodyne generators. The oscillation entering at 8 may be produced by a local generator maintained in locked synchronism with the signal wave by the method set forth in the copending application, Serial No. 574,858, filed November 13, 1931, which teaches how to produce in a receiving set an auxiliary oscillation of the same phase as the signal wave to be recorded. It is known that by combining in a detector said auxiliary oscillation with received oscillations, the latter are individually transformed into sinusoidal currents whose phases are henceforward referred to the phase of the auxiliary oscillation. In other words, S sin 2-1r'f-t designating the signal wave and B sin y w +A I an interfering wave, it is known in the art how to produce in a circuit such as 8 an auxiliary oscillationH sin 1 2-1r-f-t having the phase zv nf-f. of the signal wave; and it is known that by combining in a detector 7 said auxiliary oscillation with the whole of the received oscillations S sin 2-1r-f-t-I-EB sin[2-1r-(f|-Af)t+] the latter are transformed, in the output of the detector, into a current S-l-EB cos [2-1r-Af-t+1,b] (1) In this relation (1) which defines the whole of the detected current, the signal wave becomes a sinupass filter 9. This direct current begins and ends at the instants 1 and 2, at the same time as the oscillation 5. The change, due to this current 11 in the potential at the connection point 12 is imparted by the source 13 to the grid of the amplifying tube 14. The amplifying tube 14 has its input circuit connected with the output of the low pass filter 9. The anode circuit 48 of tube 14, in which the current illustrated in Fig. 4 is amplified, contains a resistance 15 having a value R. The output circuit 48 also includes a doublepole reversing switch 16 which may consist of the sectors of the rotary distributor of the receiving station. The switch 16 has alternately the positions 19-20, thus placing the condenser 17, having a capacity C, in parallel respectively with the resistance 15 and with the recording relay 18. By construction, the time-constant R C of the aperiodic circuit constituted by resistance 15 and condenser 17 is given a much greater value than the time 1-2, 2-3, 3-4, etc., of each unit sign of the signal. The position 19 is occupied by the reversing switch 16 during the intervals of time 21-22, 25-26, etc., (Fig. 1); these are preferably somewhat shorter, and practically coincide with the time intervals 1-2, 3-4, etc., corresponding to the signs which proceed successively in pairs. The small difierencesbetweensuch time intervals as 1-2 depending upon the transmitting distributor, and the time intervals such as 21-22 depending upon the receiving distributor, serve to take account of the small angular errors which may affeet the relative angular setting of said distributors. The duration of the intervals 21-22, 25-26 etc., has a known andconstant value T as it depends upon the receiving distributor. While the distributor 16 has this position 19, the anode circuit of the valve 14 is in fact carrying the current 11 (Fig. 4) due to the oscillation (Fig. 2) and the condenser 1'1 -is'- charged by this current. By virtue of the large time-constant of the circuit 15-17, this charge is practically proportional to the time, and thus the quantity of electricity which accumulates may be represented, relatively at the time, by the straight line 29 (Fig. 5) which shows the charge increasing and the corresponding variation of potential; thus, the potential oi the upper terminal 36 of the resistance 15 has varied from the normal value represented, by the level 21, 25 to another value represented by the level 30. At the instant 22 (Fig; 5) the reversing switch 16 automatically leaves the contact piece 19 and moves towards the contact piece 20 this movement occupies the interval 22-23, during which interval the condenser 17, whose circuit is open, preserves the potential 30 it has acquired (Fig. 5). From the instant 23 to the instant 24, the reversing switch 16 has the position 20 and the condenser 17 is connected through the-recording relay 18 with a tap 35, the potential of which is, once for all, adjusted with respect to the source 49 so as to be the same as the normal potential represented by the level 21, (Fig. 5) thus the condenser 1'7, the potential of which has previously reached the value 30, discharges into the recording relay according to the exponential curve 31. This discharge actuates the relay 18, which records the dot already transmitted between the instants 1 and 2. The relay 18 is given a resistance such that at the instant 24 at which the switch 16 leaves the contact-piece 20, the condenser 17 will be completely discharged. The condenser has thus returned to the initial state and is now able to accumulate the current produced by the dot which is to be eventually trans mitted between the instants 3 and 4. It is therefore, shown by the preceding thatithe condenser.

17 assures the recording of one sign or unit out of two, that is the dots (or spaces) occupying the 1 In order to adjust the tap 35, reception of the signal must be stopped, thus the potential of the terminal 36 of the resistance takes the normal value represented by the line 21-25 on Fig. 5. The reversing switch 38' is temporarily placed upon the contact 39, and the said tap 35 adjusted with respect to potential source 49 in such position that the voltmeter 40 indicates zero. The said switch 38 isthen moved to the contact 41, and the receiver is ready for operation. I may provide a system of potentiometersupon which the adjustable tap 35 may operate in lieu of the directconnection to the potential source shown.

Another aim of my invention is to protect the signal in the best possible way against interfering waves. According to relation (1) each of said interfering waves B sin [2-r(f+Af)-t+] did produce, by interfering in detector '7 with the auxiliary oscillation H sin 2-1r-f-t an undesired current B cos (Z-ar-Aft-i-dv). The protection of signal S against said disturbing currents is wholly insured by the combination of two conditions: The first condition consists in using for all the signals which are simultaneously transmitted, the same division of time, as represented by the instants 1, 2, 3, 4, etc., (Fig. 1) and this is done by associating together, mechanically or electrically, all of the rotary distributors used for the transmission. In this event, the signals will in fact utilize the same intervals 1-2, 2-3, 3- 4, etc., and each signal now consists in the distribution in such intervals of the unit signs corresponding to the characters in the telegram to be transmitted.

The second conditiomconsists in giving to each signal one or more determined frequencies, and in leaving between suclifrequencies suitable differences A! which are integral multiples of the number 1 As before, 'r is the duration, in seconds, of the intervals of time 21-22, 23-24, 25-26, etc., (Fig.

1) during which the distributors of the receiving apparatus connect the condensers such as 17 or 32 with the output of the receiving amplifier such as illustrated at 14. Since this duration T is substantially equal to that of 1-2, 2-3, 3 4, 6170., used for the signs themselves, the differences maintained between-the frequencies used respectively for the various signal waves will be substantially integral multiples of the frequency i or (f-i-AI) is intended for a second receiver, not shown. None of the means hitherto known will :permit the separation oft'wo signals whose frequencies are so close together, and thus the receiver shown in Fig. 3 will receive at the same time, at 6, the signal whose frequency is I and the interfering signal whose frequency is The method of receiving the signal is carried out as described above. tering signal is obtained as follows: When combining in the detector tube '7 the local oscillation having a frequency I which enters at 8 with the oscillation whose frequency is which forms for instance a dot of the interfering signal transmitted during the time interval 1-2, asinusoidal current 42 (Fig. 6) whose frequency is form depends upon the phase of the current 42 a at the instant 21 at which the charging of the condenser begins; but whatever be this form, the ordinate of the curve 43 will necessarily have a zero value at the final instant 22. Thus at the instant 23, the reversing switch 16 connects the condenser '17 with the relay 18, and this relay 18 is not actuated by the interfering signal, so that the effect of the interfering signal is thereby eliminated. The same will be true for other signals which are simultaneously transmitted by frequencies (ewe)- While I have described my invention in certain of its preferred embodiments I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. In a system of telegraphy in which the transmission time is subdivided into intervals of equal duration, said intervals being employed for the transmission of unit signs'of several signals, on different wave frequencies, a separate circuit for the reception of each of said signals, said circuit including a detector, means for impressing on said detector an auxiliary oscillation having the same frequency and approximately the'same phase as the signal wave which is to be received in said separate circuit, whereby said signal wave is transformed into a direct current. a coupling resistance, a pair of condensers, each of which form alternately in combination with said resistance an aperiodic circuit whose time constant exceeds the duration of each unit sign, a recording apparatus, a distributor connecting the coupling resistance with one of said condensers to selectively store in said condenser the quantity of electricity produced by said direct current, while the The elimination of the in-' other condenser is electrically connected with the recording apparatus, and successively alternating said connections in accordance with the division of the transmission time.

2. A method of multiplex telegraphy for the simultaneous transmission of several signals constituted by unit signs such as spaces and marking waves,'and for the separate reception of each of said signals, which comprises, transmitting the said unit signs according to a same uniform time subdivision, whereby the frequency of the unit signs is the same for all the signals, allotting to each signal wave a frequency which differs from the other wave frequencies in an integralmultiple of the said unit signs frequency, selecting separately each marking wave of the signal which is to be received by selectively storing its total accumulative effect, which effect increases arithmetically according to the rules of resonance'from the beginning to the end of said marking waves, whereas the final accumulative effect of the signs carried by the other allotted waves is null, and recording the accumulative effect of said marking wave at the instant where said marking wave is ending.

3. In a system of telegraphic communication utilizing a signal wave, and time intervals of same duration for transmitting the unit signs, a detector, means for applying to the input of said detector the said signal wave and an auxiliary oscillation which preserves with respect to the signal wave an approximately constant phase difference, thus constituting a homodyne receiver, a low pass filter interconnecting the output of said detector and the input of an amplifier vacu- I um'tube. a resistance in the output of said vacuum tube, a condenser forming when combined with said resistance and with said homodyne receiver a device selecting the frequency of the signal wave, the time constant of this device exceeding the duration of each said time interval, a recording relay, a distributor interconnecting said condenser alternately for a given time interval with said resistance and with said relay for the succeeding time interval. I

4. In a multiplex telegraphic communication system utilizing signal waves and the same transmission-time subdivision for the unit signs of all the signals simultaneously transmitted, the frequency allotted to one of said signal waves differing from the other frequencies by an intergral multiple of the frequency of the unit signs, a separate circuit for the reception of each of said signal waves, said circuit including a detector, means for impressing on said detector an auxiliary oscillation which preserves with respect to said signal wave an approximately constant phase difference, thus constituting a homodyne receiver, a resistance, a pair of condensers each in turn forming in combination with said resistance and with said homodyne receiver a device selecting the frequency of said signal oscillation, the time constant of this device exceeding largely the duration of each unit sign, a recording apparatus, a distributor effecting a connection between one of said condensers and the resistance, while the other condenser is electrically connected with the recording apparatus, and successively alternating the said connections in accordance with the division'of the transmission time. HENRI JEAN JOSEPH MARIE n1:

REGNAULD or: BELLESCIZE. 

